Method and device for decoding video

ABSTRACT

The present invention discloses a video decoding method performed by a video decoding device. The video decoding method according to an embodiment may include the steps of: obtaining NAL unit type information indicating a type of a current network abstraction layer (NAL) unit from a bitstream; and decoding, when the NAL unit type information indicates that the NAL unit type of the current NAL unit is an encoded data for an slice, the slice based on whether a mixed NAL unit type is applied to a current picture.

TECHNICAL FIELD

The present invention relates to a subpicture split method for synthesiswith other sequences and a slice split method for bitstream packing.

BACKGROUND ART

User demand on high-resolution, high-quality video are increasing. Asencoded data of a high-resolution video has a larger amount ofinformation than encoded data of a low-resolution or medium-resolutionvideo, cost for transmitting or storing the data increases.

In order to solve such a problem, researches on encoding and decodingmethods for effectively reducing the amount of encoded data ofhigh-resolution video is continued.

DISCLOSURE OF INVENTION Technical Problem

Therefore, the present invention has been made in view of the aboveproblems, and it is an object of the present invention to provide asubpicture split method for synthesis with other sequences and a slicesplit method for bitstream packing.

Technical Solution

To accomplish the above object, according to one aspect of the presentinvention, there is provided a video decoding method performed by avideo decoding device, the method comprising the steps of: obtaining NALunit type information indicating a type of a current network abstractionlayer (NAL) unit from a bitstream; and decoding, when the NAL unit typeinformation indicates that the NAL unit type of the current NAL unit isan encoded data for an slice of a picture, the slice based on whether amixed NAL unit type is applied to a current picture. Here, the step ofdecoding the slice may be performed by determining whether the NAL unittype of the current NAL unit indicates an attribute of a subpicture forthe current slice, based on whether the mixed NAL unit type is applied.

A video decoding device according to an embodiment of the presentinvention for solving the problems described above is a video decodingdevice comprising a memory and at least one processor, and the at leastone processor may obtain NAL unit type information indicating a type ofa current network abstraction layer (NAL) unit from a bitstream; anddecode, when the NAL unit type information indicates that the NAL unittype of the current NAL unit is an encoded data for an slice, the slicebased on whether a mixed NAL unit type is applied to a current picture.At this point, decoding of the slice may be performed by determiningwhether the NAL unit type of the current NAL unit indicates an attributeof a subpicture for the current slice, based on whether the mixed NALunit type is applied.

In addition, a video encoding method performed by a video encodingdevice according to an embodiment of the present invention for solvingthe problems described above may comprise the steps of: determining,when a current picture is encoded based on a mixed NAL unit type, a typeof subpicture for splitting the picture; and generating a current NALunit by encoding at least one current slice constituting the subpicturebased on the type of the subpicture. Here, the step of encoding at leastone current slice may be performed by encoding, when the current pictureis encoded based on the mixed NAL unit type, an slice so that the NALunit type of the current NAL unit indicates an attribute of thesubpicture for the current slice.

In addition, a transmission method according to an embodiment of thepresent invention for solving the above problems may transmit abitstream generated by the video encoding device or the video encodingmethod of the present disclosure.

In addition, a computer-readable recording medium according to anembodiment of the present invention for solving the above problems maystore bitstreams generated by the video encoding method or the videoencoding device of the present disclosure.

Advantageous Effects

The present invention proposes a method of generating a picture throughsynthesis with several other sequences. A picture in a sequence is splitinto a plurality of subpictures, and a new picture is generated bysynthesizing split subpictures of other pictures.

According to application of the present invention, network abstractionlayer (NAL) unit type values for two or more subpictures constituting apicture may be different from each other. This has an advantage ofeasily constituting/synthesizing a video since it does not need toequally set the NUTs of a plurality of subpictures constituting onesheet of video when synthesizing different contents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view schematically showing the configuration of a videoencoding device to which the present invention may be applied.

FIG. 2 is a view showing an example of a video encoding method performedby a video encoding device.

FIG. 3 is a view schematically showing the configuration of a videodecoding device to which the present invention may be applied.

FIG. 4 is a view showing an example of a video decoding method performedby a decoding device.

FIG. 5 is a view showing an example of a NAL packet for a slice.

FIG. 6 is a view showing an example of a hierarchical GOP structure.

FIG. 7 is a view showing an example of a display output order and adecoding order.

FIG. 8 is a view showing an example of a leading picture and a normalpicture.

FIG. 9 is a view showing an example of a RASL picture and a RADLpicture.

FIG. 10 is a view showing syntax for a slice segment header.

FIG. 11 is a view showing an example of a contents synthesizing process.

FIG. 12 is a view showing an example of a subpicture ID and a sliceaddress.

FIG. 13 is a view showing an example of a NUT for each subpicture/slice.

FIG. 14 is a view showing an embodiment of syntax of a picture parameterset (PPS).

FIG. 15 is a view showing an embodiment of syntax of a slice header.

FIG. 16 is a view showing syntax of a picture header structure.

FIG. 17 is a view showing syntax for obtaining a reference picture list.

FIG. 18 is a view showing an example of synthesizing contents.

FIGS. 19 and 20 are flowcharts illustrating a decoding method and anencoding method according to an embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Since the present invention may make various modifications and providevarious embodiments, specific embodiments will be illustrated in thedrawings and described in detail. However, this is not intended to limitthe present invention to the specific embodiments. The terms used inthis specification are used only to describe the specific embodimentsand not intended to limit the technical spirit of the present invention.Singular expressions include plural expressions unless the contextclearly indicates otherwise. It should be understood that in thisspecification, terms such as “include”, “have” and the like are intendedto indicate existence of features, numbers, steps, operations,components, parts, or combinations thereof described in thespecification, and the possibility of existence or addition of one ormore other features, numbers, steps, operations, components, parts orcombinations thereof are not excluded in advance.

Meanwhile, each of the components in the drawings described in thepresent invention is independently illustrated for convenience ofdescription on different characteristic functions and does not mean thateach of the components is implemented as separate hardware or software.For example, two or more components may be combined to form onecomponent, or one component may be divided into a plurality ofcomponents. Embodiments in which each component is integrated and/orseparated are also included in the scope of the present invention as faras it does not depart from the essence of the present invention.

Hereinafter, preferred embodiments of the present invention will bedescribed in more detail with reference to the accompanying drawings.Hereinafter, the same reference numerals are used for the samecomponents in the drawings, and duplicate descriptions for the samecomponents are omitted.

Meanwhile, the present invention relates to video coding. For example,the methods/embodiments disclosed in the present invention may beapplied to the methods disclosed in the versatile video coding (VVC)standard, the Essential Video Coding (EVC) standard, the AOMedia Video 1(AV1) standard, the 2nd generation of audio video coding (AVS2)standard, or a next-generation video coding standard (e.g., H.267,H.268, etc.).

In this specification, an access unit (AU) means a unit representing aplurality of picture sets belonging to different layers output from adecoded picture buffer (DPB) at the same time. A picture generally meansa unit representing a video in a specific time period, and a slice is aunit constituting a part of a picture in coding. One picture may beconfigured of a plurality of slices, and if needed, the picture and theslice may be interchangeably used.

A pixel or a pel may mean a minimum unit constituting one picture (orvideo). In addition, ‘sample’ may be used as a term corresponding to thepixel. Generally, a sample may represent a pixel or a pixel value andmay represent only a pixel/pixel value of a luma component or mayrepresent only a pixel/pixel value of a chroma component.

A unit represents a basic unit of video processing. The unit may includeat least one among a specific area of a picture and information relatedto a corresponding area. The unit and the terms such as a block or anarea may be interchangeably used depending on circumstances. Generally,an M×N block may represent a set of samples or transform coefficientsconfigured of M columns and N rows.

FIG. 1 is a view schematically showing the configuration of a videoencoding device to which the present invention may be applied.

Referring to FIG. 1, a video encoding device 100 may include a picturepartition unit 105, a prediction unit 110, a residual processing unit120, an entropy encoding unit 130, an addition unit 140, a filter unit150, and a memory 160. The residual processing unit 120 may include asubtraction unit 121, a transform unit 122, a quantization unit 123, arearrangement unit 124, an inverse quantization unit 125, and an inversetransform unit 126.

The picture partition unit 105 may split an input picture into at leastone processing unit.

For example, a processing unit may be referred to as a coding unit (CU).In this case, the coding unit may be recursively split from a codingtree unit according to a quad-tree binary-tree (QTBT) structure. Forexample, one coding tree unit may be split into a plurality of nodes ofdeeper depth based on a quad tree structure and/or a binary treestructure. In this case, for example, the quad tree structure may beapplied first, and the binary tree structure may be applied later.Alternatively, the binary tree structure may be applied first. Decodingmay be performed on a node that is not split any more, and a coding unitmay be determined for a node that is not split any more as describedabove. Since the coding tree unit is a unit for splitting a coding unit,the coding tree unit may be referred to as a coding unit. In this case,the coding tree unit may be referred to as a largest coding unit (LCU)since the coding unit is determined by split of the coding tree unit.

As described above, a coding procedure according to the presentinvention may be performed based on a final coding unit that is notsplit any more. In this case, the coding tree unit itself may be used asa final coding unit based on coding efficiency or the like according tovideo characteristics, or a coding unit may be recursively split intocoding units of a further deeper depth as needed, and a coding unit ofan optimal size may be used as a final coding unit. Here, the codingprocedure may include a procedure such as prediction, transform,reconstruction or the like described below.

As another example, a processing unit may include a coding unit (CU), aprediction unit (PU), or a transform unit (TU). The coding unit may besplit from a coding tree unit into coding units of deeper depthaccording to a quad tree structure. In this case, the coding tree unititself may be used as a final coding unit based on coding efficiency orthe like according to video characteristics, or a coding unit may berecursively split into coding units of a further deeper depth as needed,and a coding unit of an optimal size may be used as a final coding unit.When a minimum coding unit (min CU) is set, a coding unit may not besplit into coding units smaller than the minimum coding unit. Here, afinal coding unit means a coding unit that functions as a basis forbeing partitioned or split into prediction units or transform units. Theprediction unit is a unit partitioned from a coding unit and may be aunit of sample prediction. At this point, the prediction unit may besplit into subblocks. The transform unit may be split from a coding unitaccording to a quad tree structure and may be a unit for inducing atransform coefficient and/or a unit for inducing a residual signal fromthe transform coefficient. Hereinafter, the coding unit may be referredto as a coding block (CB), the prediction unit may be referred to as aprediction block (PB), and the transform unit may be referred to as atransform block (TB). A prediction block or a prediction unit may mean aspecific area of a block shape within a picture and may include an arrayof prediction samples. In addition, a transform block or transform unitmay mean a specific area of a block shape within a picture and mayinclude an array of transform coefficients or residual samples.

The prediction unit 110 may perform prediction on a processing targetblock (hereinafter, referred to as a current block) and generate apredicted block including prediction samples for the current block. Theunit of prediction performed by the prediction unit 110 may be a codingblock, a transform block, or a prediction block.

The prediction unit 110 may determine whether intra prediction or interprediction is applied to the current block. For example, the predictionunit 110 may determine whether intra prediction or inter prediction isapplied by the unit of CU.

In the case of intra prediction, the prediction unit 110 may derive aprediction sample for the current block based on a reference sampleoutside the current block in a picture to which the current blockbelongs (hereinafter, referred to as a current picture). At this point,the prediction unit 110 may (i) derive a prediction sample based on anaverage or interpolation of neighboring reference samples of the currentblock, and (ii) derive the prediction sample based on a reference sampleexisting in a specific (prediction) direction with respect to theprediction sample among the neighboring reference samples of the currentblock. The case of (i) may be referred to as a non-directional mode or anon-angular mode, and the case of (ii) may be referred to as adirectional mode or an angular mode. In the intra prediction, aprediction mode may have, for example, 33 directional prediction modesand at least two non-directional modes. The non-directional mode mayinclude a DC prediction mode and a planar mode. The prediction unit 110may determine a prediction mode applied to the current block by usingthe prediction mode applied to neighboring blocks.

In the case of inter prediction, the prediction unit 110 may derive aprediction sample for the current block based on a sample specified by amotion vector on a reference picture. The prediction unit 110 may derivea prediction sample for the current block by applying any one among askip mode, a merge mode, and a motion vector prediction (MVP) mode. Inthe case of the skip mode and the merge mode, the prediction unit 110may use motion information of a neighboring block as motion informationof the current block. In the case of the skip mode, unlike the mergemode, the difference (residual) between the prediction sample and theoriginal sample is not transmitted. In the case of the MVP mode, amotion vector of the current block may be derived using a motion vectorof a neighboring block as a motion vector predictor of the currentblock.

In the case of inter prediction, the neighboring block may include aspatial neighboring block existing in the current picture and a temporalneighboring block existing in a reference picture. The reference pictureincluding the temporal neighboring block may be referred to as acollocated picture (colPic). The motion information may include a motionvector and a reference picture index. Information such as predictionmode information and motion information may be (entropy) encoded andoutput in the form of a bitstream.

When motion information of a temporal neighboring block is used in theskip mode and the merge mode, the highest picture on a reference picturelist may be used as a reference picture. Reference pictures included inthe reference picture list may be arranged based on a difference in thepicture order count (POC) between the current picture and the referencepicture. The POC corresponds to the display order of pictures and may bedistinguished from the coding order.

The subtraction unit 121 generates a residual sample, which is adifference between an original sample and the prediction sample. Whenthe skip mode is applied, the residual sample may not be generated asdescribed above.

The transform unit 122 generates a transform coefficient by transformingthe residual sample by the unit of transform block. The transform unit122 may perform transform according to the size of a correspondingtransform block and a prediction mode applied to a coding block or aprediction block spatially overlapped with the transform block. Forexample, when intra prediction is applied to the coding block or theprediction block overlapped with the transform block, and the transformblock is a 4×4 residual array, the residual sample is transformed usinga Discrete Sine Transform (DST) transform kernel, and in other cases,the residual sample may be transformed using a Discrete Cosine Transform(DST) transform kernel.

The quantization unit 123 may generate quantized transform coefficientsby quantizing transform coefficients.

The rearrangement unit 124 rearranges the quantized transformcoefficients. The rearrangement unit 124 may rearrange the quantizedtransform coefficients of a block shape in the form of a one-dimensionalvector through a coefficient scanning method. Here, although therearrangement unit 124 is described as a separate configuration, therearrangement unit 124 may be a part of the quantization unit 123.

The entropy encoding unit 130 may perform entropy encoding on thequantized transform coefficients. The entropy encoding may include, forexample, encoding methods such as exponential Golomb, context-adaptivevariable length coding (CAVLC), context-adaptive binary arithmeticcoding (CABAC), and the like. The entropy encoding unit 130 may encodeinformation needed for video reconstruction (e.g., a value of a syntaxelement, etc.) together or separately, in addition to the quantizedtransform coefficients. The entropy-encoded information may betransmitted or stored in the form of a bitstream by the unit of networkabstraction layer (NAL).

The inverse quantization unit 125 performs inverse-quantization on thevalues quantized by the quantization unit 123 (quantized transformcoefficients), and the inverse transform unit 126 generates a residualsample by performing inverse-transform on the values inverse-quantizedby the inverse quantization unit 125.

The addition unit 140 reconstructs a picture by adding the residualsample and the prediction sample. The residual sample and the predictionsample may be added by the unit of block to generate a reconstructedblock. Here, although the addition unit 140 is described as a separateconfiguration, the addition unit 140 may be a part of the predictionunit 110. Meanwhile, the addition unit 140 may be referred to as areconstruction unit or a reconstructed block generation unit.

For a reconstructed picture, the filter unit 150 may apply a deblockingfilter and/or a sample adaptive offset. Through the deblocking filterand/or the sample adaptive offset, an artifact of a block boundary inthe reconstructed picture or distortion in the quantization process maybe corrected. The sample adaptive offset may be applied by the unit ofsample and may be applied after the process of deblocking filtering iscompleted. The filter unit 150 may apply an adaptive loop filter (ALF)to the reconstructed picture. The ALF may be applied to a reconstructedpicture after applying the deblocking filter and/or the sample adaptiveoffset.

The memory 160 may store the reconstructed picture (the decoded picture)or information needed for encoding/decoding. Here, the reconstructedpicture may be a reconstructed picture for which a filtering procedurehas been completed by the filter unit 150. The stored reconstructedpicture may be used as a reference picture for (inter) prediction ofother pictures. For example, the memory 160 may store (reference)pictures used for inter prediction. At this point, the pictures used forinter prediction may be specified by a reference picture set or areference picture list.

FIG. 2 is a view showing an example of a video encoding method performedby a video encoding device. Referring to FIG. 2, the video encodingmethod may include processes of block partitioning, intra/interprediction, transform, quantization, and entropy encoding. For example,a current picture may be split into a plurality of blocks, and aprediction block of the current block may be generated throughintra/inter prediction, and a residual block of the current block may begenerated through subtraction of the input block of the current blockand the prediction block. Thereafter, a coefficient block, i.e.,transform coefficients of the current block, may be generated throughtransform of the residual block. The transform coefficients may bequantized, entropy encoded, and stored in a bitstream.

FIG. 3 is a view schematically showing the configuration of a videodecoding device to which the present invention may be applied.

Referring to FIG. 3, a video decoding device 300 may include an entropydecoding unit 310, a residual processing unit 320, a prediction unit330, an addition unit 340, a filter unit 350, and a memory 360. Here,the residual processing unit 320 may include a rearrangement unit 321,an inverse quantization unit 322, and an inverse transform unit 323.

When a bitstream including video information is input, the videodecoding device 300 may reconstruct a video in response to a process inwhich video information is processed by the video encoding device.

For example, the video decoding device 300 may perform video decodingusing a processing unit applied in the video encoding device.Accordingly, the processing unit block of video decoding may be, forexample, a coding unit, and as another example, it may be a coding unit,a prediction unit, or a transform unit. The coding unit may be splitfrom a coding tree unit according to a quad tree structure and/or abinary tree structure.

A prediction unit and a transform unit may be further used in somecases, and in this case, the prediction block is a block derived orpartitioned from a coding unit and may be a unit of sample prediction.At this point, the prediction unit may be split into subblocks. Thetransform unit may be split from a coding unit according to a quad treestructure and may be a unit for inducing a transform coefficient or aunit for inducing a residual signal from the transform coefficient.

The entropy decoding unit 310 may parse a bitstream and outputinformation needed for video reconstruction or picture reconstruction.For example, the entropy decoding unit 310 may decode information in abitstream based on a coding method such as exponential Golomb coding,CAVLC, or CABAC, and output a value of a syntax element needed for videoreconstruction, and quantized values of transform coefficients relatedto the residual.

More specifically, the CABAC entropy decoding method may receive a bincorresponding to each syntax element from a bitstream, determine acontext model using syntax element information of a decoding target anddecoding information of neighboring and decoding target blocks or usinginformation on the symbol/bin decoded in a previous step, and generate asymbol corresponding to a value of each syntax element by performingarithmetic decoding on the bin after predicting a probability ofoccurrence of the bin according to the determined context model. At thispoint, the CABAC entropy decoding method may update the context model byusing information on the decoded symbol/bin for the sake of the contextmodel of a next symbol/bin after the context model is determined.

Among the information decoded by the entropy decoding unit 310,information on prediction is provided to the prediction unit 330, andthe residual value on which entropy decoding is performed by the entropydecoding unit 310, i.e., the quantized transform coefficient, may beinput into the rearrangement unit 321.

The rearrangement unit 321 may rearrange the quantized transformcoefficients in the form of a two-dimensional block. The rearrangementunit 321 may perform rearrangement in response to coefficient scanningperformed by the encoding device. Here, although the rearrangement unit321 is described as a separate configuration, the rearrangement unit 321may be a part of the inverse quantization unit 322.

The inverse quantization unit 322 may inverse quantize the quantizedtransform coefficients based on (inverse) quantization parameters andoutput transform coefficients. At this point, information for derivingthe quantization parameters may be signaled from the encoding device.

The inverse transform unit 323 may derive residual samples by performinginverse transform on the transform coefficients.

The prediction unit 330 may perform prediction on the current block andgenerate a predicted block including prediction samples for the currentblock. The unit of prediction performed by the prediction unit 330 maybe a coding block, a transform block, or a prediction block.

The prediction unit 330 may determine whether to apply intra predictionor inter prediction based on the information on the prediction. At thispoint, the unit for determining which of the intra prediction and theinter prediction to apply may be different from the unit for generatinga prediction sample. In addition, in inter prediction and intraprediction, the units for generating a prediction sample may also bedifferent. For example, whether to apply inter prediction or intraprediction may be determined by the unit of CU. In addition, forexample, in inter prediction, a prediction mode may be determined, and aprediction sample may be generated by the unit of PU. In intraprediction, a prediction mode may be determined by the unit of PU, and aprediction sample may be generated by the unit of TU.

In the case of intra prediction, the prediction unit 330 may derive aprediction sample for the current block based on neighboring referencesamples in the current picture. The prediction unit 330 may derive theprediction sample for the current block by applying a directional modeor a non-directional mode based on the neighboring reference samples ofthe current block. At this point, a prediction mode to be applied to thecurrent block may be determined by using the intra prediction mode of aneighboring block.

In the case of inter prediction, the prediction unit 330 may derive aprediction sample for the current block based on a sample specified on areference picture by a motion vector on the reference picture. Theprediction unit 330 may derive the prediction sample for the currentblock by applying any one among a skip mode, a merge mode, and an MVPmode. At this point, motion information needed for inter prediction ofthe current block provided by the video encoding device, such asinformation on the motion vector, the reference picture index and thelike, may be obtained or derived based on information on the prediction.

In the case of the skip mode and the merge mode, motion information of aneighboring block may be used as motion information of the currentblock. At this point, the neighboring block may include a spatialneighboring block and a temporal neighboring block.

The prediction unit 330 may construct a merge candidate list by usingmotion information of available neighboring blocks and may useinformation indicated by a merge index in the merge candidate list as amotion vector of the current block. The merge index may be signaled fromthe encoding device. The motion information may include a motion vectorand a reference picture. When motion information of a temporalneighboring block is used in the skip mode and the merge mode, thehighest picture in the reference picture list may be used as thereference picture.

In the case of the skip mode, the difference (residual) between theprediction sample and the original sample is not transmitted unlike themerge mode.

In the case of the MVP mode, a motion vector of the current block may bederived by using a motion vector of a neighboring block as a motionvector predictor. At this point, the neighboring block may include aspatial neighboring block and a temporal neighboring block.

For example, when the merge mode is applied, the merge candidate listmay be generated by using a motion vector of a reconstructed spatialneighboring block and/or a motion vector corresponding to a Col block,which is a temporal neighboring block. In the merge mode, the motionvector of a candidate block selected from the merge candidate list isused as the motion vector of the current block. The information on theprediction may include a merge index indicating a candidate block havingan optimal motion vector selected among candidate blocks included in themerge candidate list. At this point, the prediction unit 330 may derivea motion vector of the current block by using the merge index.

As another example, when the Motion Vector Prediction (MVP) mode isapplied, a motion vector predictor candidate list may be generated byusing a motion vector of a reconstructed spatial neighboring blockand/or a motion vector corresponding to a Col block, which is a temporalneighboring block. That is, the motion vector of a reconstructed spatialneighboring block and/or the motion vector corresponding to a Col block,which is a temporal neighboring block, may be used as a motion vectorcandidate. The information on the prediction may include a predictionmotion vector index indicating an optimal motion vector selected amongthe motion vector candidates included in the list. At this point, theprediction unit 330 may select a prediction motion vector of the currentblock among the motion vector candidates included in the motion vectorcandidate list by using the motion vector index. The prediction unit ofthe encoding device may obtain a motion vector difference (MVD) betweenthe motion vector of the current block and the motion vector predictorand encode and output the motion vector difference in the form of abitstream. That is, the MVD may be obtained by subtracting the motionvector predictor from the motion vector of the current block. At thispoint, the prediction unit 330 may obtain the motion vector differenceincluded in the information on the prediction and derive the motionvector of the current block through addition of the motion vectordifference and the motion vector predictor. The prediction unit may alsoobtain or derive a reference picture index or the like indicating thereference picture from the information on the prediction.

The addition unit 340 may reconstruct the current block or the currentpicture by adding the residual sample and the prediction sample. Theaddition unit 340 may reconstruct the current picture by adding theresidual sample and the prediction sample by the unit of block. When theskip mode is applied, as the residual is not transmitted, the predictionsample may become a reconstructed sample. Here, although the additionunit 340 is described as a separate configuration, the addition unit 340may be a part of the prediction unit 330. Meanwhile, the addition unit340 may be referred to as a reconstruction unit or a reconstructed blockgeneration unit.

The filter unit 350 may apply a deblocking filtering sample adaptiveoffset and/or an ALF to the reconstructed picture. At this point, thesample adaptive offset may be applied by the unit of sample and may beapplied after deblocking filtering. The ALF may be applied afterdeblocking filtering and/or sample adaptive offset.

The memory 360 may store the reconstructed picture (decoded picture) orinformation needed for decoding. Here, the reconstructed picture may bea reconstructed picture for which a filtering procedure has beencompleted by the filter unit 350. For example, the memory 360 may storepictures used for inter prediction. At this point, the pictures used forinter prediction may be specified by a reference picture set or areference picture list. The reconstructed picture may be used as areference picture for another picture. In addition, the memory 360 mayoutput reconstructed pictures in an output order.

FIG. 4 is a view showing an example of a video decoding method performedby a video decoding device. Referring to FIG. 4, the video decodingmethod may include the processes of entropy decoding, inversequantization, inverse transform, and intra/inter prediction. Forexample, an inverse process of the encoding method may be performed inthe decoding device. Specifically, quantized transform coefficients maybe obtained through entropy decoding of a bitstream, and a coefficientblock of the current block, i.e., transform coefficients, may beobtained through an inverse quantization process on the quantizedtransform coefficients. A residual block of the current block may bederived through inverse transform of the transform coefficients, and areconstructed block of the current block may be derived through additionof the prediction block of the current block derived through intra/interprediction and the residual block.

Meanwhile, operators in the embodiments described below may be definedas shown in the following table.

TABLE 1 Floor( x ) the largest integer less than or equal to x. Log2( u) the base-2 logarithm of u. Ceil( x ) the smallest integer greater thanor equal to x. x >> y Arithmetic right shift of a two's complementinteger representation of x by y binary digits. This function is definedonly for non-negative integer values of y. Bits shifted into the mostsignificant bits (MSBs) as a result of the right shift have a valueequal to the MSB of x prior to the shift operation. x << y Arithmeticleft shift of a two's complement integer representation of x by y binarydigits. This function is defined only for non-negative integer values ofy. Bits shifted into the least significant bits (LSBs) as a result ofthe left shift have a value equal to 0. > greater than. >= greater thanor equal to. < less than. <= less than or equal to. == equal to. ! = notequal to.

Referring to Table 1, Floor (x) may represent a maximum integer valuesmaller than or equal to x, Log 2(u) may represent a logarithmic valuewith 2 of u as the base, and Ceil (x) may represent a minimum integervalue larger than or equal to x. For example, in the case of Floor(5.93), since the maximum integer value smaller than or equal to 5.93 is5, it may represent 5.

In addition, referring to Table 1, x>>y may represent an operator thatshifts x to the right y times, and x<<y may represent an operator thatshifts x to the left y times.

Introduction

The HEVC standard proposes two types of screen split methods.

1) Slice: It provides a function of encoding/decoding a picture bysplitting the picture in coding tree units (CTU) in a raster scan order.And, there is slice header information.

2) Tile: It provides a function of encoding/decoding a picture bypartitioning the picture into multiple columns and rows by the unit ofCTU. The partitioning method may include both equal partitioning andindividual partitioning. A header for the tile does not separatelyexist.

The slice becomes a bitstream packing unit. That is, one slice may begenerated from one network abstraction layer (NAL) bitstream. As shownin FIG. 5, a NAL packet for a slice is configured in order of NALheader, slice header, and slice data. At this point, a NAL unit type(NUT) is included in NAL header information.

NUTs for a slice proposed in the HEVC standard according to anembodiment are as shown in Table 2. In Table 2, NUTs for inter slice inwhich inter prediction is performed are 0 to 9, and NUTs for intra slicein which intra prediction is performed are 16 to 21. Here, the interslice means that it is encoded in an inter prediction method, and theintra slice means that it is encoded in an intra prediction method. Oneslice is defined to have one NUT, and a plurality of slices in a picturemay all be set to have the same NUT value. For example, when one pictureis split into 4 slices and encoded in the intra prediction method, theNUT values for all the 4 slices in the picture may be equally set to“19: IDR_W_RADL”.

TABLE 2 Content of NAL unit and nal_unit_type Name of nal_unit_type RBSPsyntax structure  0, 1 TRAIL_N, TRAIL_R Coded slice of a non-TSA,  non-STSA trailing picture  2, 3 TSA_N, TSA_R Coded slice of a TSApicture  4, 5 STSA_N, STSA_R Coded slice of an STSA picture  6, 7RADL_N, RADL_R Coded slice of an RADL picture  8, 9 RASL_N, RASL_R Codedslice of an RASL picture 16, 17,18 BLA_W_LP, BLA_W_RADL, Coded slice ofa BLA picture BLA_N_LP 19, 20 IDR_W_RADL, Coded slice of an IDR pictureIDR_N_LP 21 CRA Coded slice of a CRA picture

In Table 2, the abbreviations may be defined as shown below.

-   -   TSA (Temporal sub-layer Switching Access)    -   STSA (Step-wise Temporal sub-layer Switching Access)    -   RADL (Random Access Decodable Leading)    -   RASL (Random Access Skipped Leading)    -   BLA (Broken Link Access)    -   IDR (Instantaneous Decoding Refresh)    -   CRA (Clean Random Access)    -   LP (Leading Picture)    -   _N (No reference)    -   _R (Reference)    -   _W_LP/RADL (With LP/RADL)    -   _N_LP (No LP, without LP)

BLA, IDR, and CRA, which are NUTs for intra slice, are referred to asIntra Random Access Point (IRAP). IRAP means a picture capable of randomaccess to a position in the middle of a bitstream. That is, it refers toa picture in which the playback position may be suddenly changed duringvideo playback. The intra slice may exist only in an I slice type.

The inter slice may be classified as a P slice or a B slice according tounidirectional prediction (P: predictive) or bidirectional prediction(B: bi-predictive). The prediction and encoding process is performed bythe unit of group of pictures (GOP), and the HEVC standard performs anencoding/decoding process including prediction by using a hierarchicalGOP structure. FIG. 6 shows an example of the hierarchical GOPstructure, and each picture is classified as I, P, or B picture (slice)according to a prediction method.

Due to the characteristics of the B slice performing bidirectionalprediction and/or the hierarchical GOP structure, a decoding order and adisplay order of pictures in a sequence are different (see FIG. 7). InFIG. 7, IRAP means intra slice, B and P mean inter slice, and it may beconfirmed that the playback order and the reconstruction order have beenchanged completely.

Among the inter slices, a picture that precedes the IRAP in the playbackorder while following the IRAP in the reconstruction order is referredto as a leading picture (LP) (see FIG. 8). The LP is classified as RADLor RASL depending on situation. When random access occurs, an LP thatcan be decoded is defined as RADL, and an LP that cannot be decodedduring random access and thus the reconstruction process of acorresponding picture should be skipped is defined as RASL. In FIG. 8,pictures of the same color are defined as one GOP.

Distinction between the RADL and the RASL is determined according to theposition of a reference picture during inter screen prediction (see FIG.9). That is, the RASL means an inter picture which uses a reconstructedpicture in a GOP other than a corresponding GOP as a reference picture,or uses a picture reconstructed using a reconstructed picture in anotherGOP as a reference picture as a reference picture. In this case, it isreferred to as open GOP since the reconstructed picture in another GOPis (directly or indirectly) used as a reference picture. RASL and RADLare set as NUT information for a corresponding inter slice.

A NUT for an intra slice is classified as another intra slice NUTaccording to the NUT of an inter slice that precedes and/or follows inthe playback order and/or the reconstruction order of the correspondingintra slice. Seeing the IDR NUT, IDR may be classified as IDR_W_RADLwith RADL and IDR_N_LP without an LP. That is, IDR is a type that doesnot have an LP or a type having only RADL among the LPs, and IDR may nothave RASL. On the other hand, CRA is a type that may have both RADLand/or RASL among the LPs. That is, CRA is a type that may support openGOP.

Generally, since the intra slice performs only intra screen prediction,reference picture information for the intra slice is not required. Here,a reference picture is used for inter screen prediction. However, due tothe characteristic of the CRA NUT slice supporting an open GOPstructure, reference picture information is inserted in the NALbitstream of a corresponding CRA although a CRA slice is an intra slice.The reference picture information is information on a reference pictureto be used in an inter slice after a corresponding CRA (in the order ofreconstruction), not for being used in a corresponding CRA slice. Thisis not to remove the reference picture from the decoded picture buffer(DPB). For example, when the NUT of a corresponding intra slice is IDR,the DPB is reset. That is, all reconstructed pictures existing in theDPB at the time point are removed. FIG. 10 is a view showing syntax fora slice segment header. As shown in FIG. 10, when the NUT of acorresponding slice is not IDR, reference picture information may bedescribed in the bitstream. That is, when the NUT of a correspondingslice is CRA, reference picture information may be described.

The present invention proposes a subpicture split method for synthesiswith other sequences and a slice split method for bitstream packing.

In the present invention, a slice means an encoding/decoding area and isa data packing unit for generating one NAL bitstream. For example, asheet of picture is split into a plurality of slices, and each slice isgenerated as one NAL packet through an encoding process.

In the present invention, a subpicture is a division of area forsynthesis with other contents. FIG. 11 shows an example of synthesiswith other contents. There are three contents of white, gray and black,and an AU (access unit) of each content is divided into four slices togenerate a packet, and like the image on the right side in FIG. 11, anew image may be generated by synthesizing the upper left portion withwhite contents, the lower left portion with gray contents, and the rightportion with black contents. Here, in the white area and the gray area,one slice may be configured as one subpicture, and in the black area,two slices may be configured as one subpicture. That is, one subpicturemay include at least one slice. To generate a new image (to synthesizecontents), a Bit-stream Extractor and Merger (BEAMer) extracts areasfrom different contents by the unit of subpicture and synthesizes them.In FIG. 11, the synthesized image may be split into four slices andconfigured of three subpictures.

One subpicture means an area having the same subpicture ID and/or thesame subpicture index value. In other words, at least one slice havingthe same subpicture ID and/or the same subpicture index value may bereferred to as one subpicture area. Here, the subpicture ID and/or thesubpicture index value is included in the slice header information. Thesubpicture index value may be set in a raster scan order. FIG. 12 showsan example in which one picture is configured of 6 (rectangular) slicesand 4 subpicture areas (of different colors). Here, “A”, “B”, “C” and“D” denote examples of subpicture ID, and “0” and “1” denote sliceaddresses within a corresponding subpicture. That is, a slice addressvalue is a slice index value in the raster scan order within acorresponding subpicture. For example, “B-0” means a 0-th slice in the Bsubpicture, and “B-1” means a first slice in the B subpicture.

In the present invention, NUT values for two or more subpicturesconstituting one image may be different. For example, in FIG. 12, thewhite subpicture (slice) in one sheet of image may be an intra slice,and the gray subpicture (slice) and the black subpicture (slice) may beinter slices.

This has an advantage of easily constituting/synthesizing a video sinceit does not need to equally set the NUTs of a plurality of subpicturesconstituting a picture when synthesizing different contents. Acorresponding function may be referred to as a mixed NAL unit type in asingle picture and may be simply named as a mixed NUT.mixed_nalu_type_in_pic_flag may be used to set enabled/disabled of thecorresponding function. A corresponding flag may be defined at aposition of one or more among sequence parameter set (SPS), pictureparameter set (PPS), picture header (PH), and slice header (SH). Forexample, when the flag is defined in the PPS, the flag may be named aspps_mixed_nalu_types_in_pic_flag.

When the flag value is disabled (e.g., mixed_nalu_type_in_pic_flag==0),NUTs for all subpictures and/or slices in the corresponding picture mayhave the same value. For example, NUTs for all video coding layer (VCL)NAL units for a picture may be set to have the same value. In addition,a picture or a picture unit (PU) may be referenced to have a NUT thesame as that of a slice NAL unit encoded for the picture or pictureunit. Here, VCL means a NAL type for a slice including a slice datavalue.

On the other hand, when the flag value is enabled (e.g.,mixed_nalu_type_in_pic_flag==1), the corresponding picture may beconfigured of two or more subpictures. In addition, NUTs for thesubpictures and/or slices in the corresponding picture may have thedifferent value. In addition, when the flag value is enabled, it may berestricted so that the VCL NAL unit of the picture may not have a NUT ofGDR NUT type. In addition, when the NUT (e.g., the first NUT) of any oneVCL NAL unit (e.g., the first NAL unit) of a corresponding picture isany one among IDR_W_RADL, IDR_N_LP, and CRA_NUT, it may be restricted sothat the NUT (e.g., the second NUT) of another VCL NAL unit (e.g., thesecond NAL unit) of the picture may be set to any one among IDR_W_RADL,IDR_N_LP, CRA_NUT, and TRAIL_NUT. For example, it may be restricted sothat the second NUT may be set to one value among the first NUT and theTRAIL_NUT.

An example in which VCL NAL units of the corresponding picture have atleast two different NUT values will be described with reference to FIGS.12 and 13. In an embodiment, two or more subpictures may have two ormore different NUT values. At this point, it may be restricted so thatthe NUT values for all slices included in one subpicture are the same.For example, as shown in FIG. 13, NUT values for the two slices insubpicture B of FIG. 12 may be equally set to CRA, and NUT values forthe two slices in subpicture C may be equally set to TRAIL, andsubpictures A, B, C, and D may be set to have at least two or moredifferent NUT values. Accordingly, as shown in FIG. 13, the NUT valuefor the slices in subpictures A, C and D is TRAIL, and it may be set tohave a NUT value different from CRA, which is the NUT of subpicture B.

In the present invention, the NUTs for intra slice and inter slice maybe specified as shown in Table 3. As shown in the embodiment of Table 3,definitions and functions for RADL, RASL, IDR, CRA and the like may beset in the same manner as shown in the HEVC standard (Table 1). In thecase of Table 3, a mixed NUT type is added. In Table 3, the value‘disabled’ (e.g., 0) of mixed_nalu_type_in_pic_flag may represent a NUTfor a slice in a picture (in the same manner as HEVC), and the value‘enabled’ (e.g., 1) of mixed_nalu_type_in_pic_flag may represent a NUTfor a slice in a subpicture. For example, when the value ofmixed_nalu_type_in_pic_flag is 0 and the NUT of the VCL NAL unit isTRAIL_NUT, the NUT of the current picture may be identified asTRAIL_NUT, and the NUT of another subpicture belonging to the currentpicture may also be derived as TRAIL_NUT. In addition, when the value ofmixed_nalu_type_in_pic_flag is 1 and the NUT of the VCL NAL unit isTRAIL_NUT, the NUT of the current subpicture may be identified asTRAIL_NUT, and the NUT of at least one among other subpictures belongingto the current picture may be predicted as not being TRAIL_NUT.

TABLE 3 NAL unit Name of nal_unit_type Content of NAL unit and RBSPsyntax structure type class TRAIL_NUT Coded slice of a trailing pictureor subpicture* VCL slice_layer_rbsp( ) STSA_NUT Coded slice of an STSApicture or subpicture* VCL slice_layer_rbsp( ) RADL_NUT Coded slice of aRADL picture or subpicture* VCL slice_layer_rbsp( ) RASL_NUT Coded sliceof a RASL picture or subpicture* VCL slice_layer_rbsp( ) IDR_W_RADLCoded slice of an IDR picture or subpicture* VCL IDR_N_LPslice_layer_rbsp( ) CRA_NUT Coded slice of a CRA picture or subpicture*VCL silce_layer_rbsp( ) GDR_NUT Coded slice of a GDR picture orsubpicture* VCL slice_layer_rbsp( )

 mixed_nal_unit_types_in_pic

 

mixed_nal_unit_types_in_pic

 

*represents the attribute of a picture when the value ofmixed_nal_unit_types_in_pic is 0 and represents the attribute of asubpicture when the value of mixed_nal_unit_types_in_pic is 1.

As described above, in the case where the value ofmixed_nalu_type_in_pic_flag indicates enabled (e.g., 1), when any oneVCL NAL unit (e.g., the first NAL unit) belonging to one picture has anyone value among IDR_W_RADL, IDR_N_LP, and CRA_NUT as a NUT (e.g., thefirst NUT), at least one VCL NAL unit (e.g., the second NAL unit) amongother VCL NAL units of the picture may have any one NUT value, otherthan the first NUT, among IDR_W_RADL, IDR_N_LP, CRA_NUT, and TRAIL_NUTas a NUT (e.g., the second NUT).

In this manner, when a VCL NAL unit (e.g., the first NAL unit) for thefirst subpicture belonging to one picture has any one value amongIDR_W_RADL, IDR_N_LP, and CRA_NUT as a NUT (e.g., a first NUT), the VCLNAL unit (e.g., a second NAL unit) for the second subpicture of thecorresponding picture may have any one NUT value, other than the firstNUT, among IDR_W_RADL, IDR_N_LP, CRA_NUT, and TRAIL_NUT as a NUT (e.g.,a second NUT).

For example, when the value of mixed_nalu_type_in_pic_flag indicatesactivation (e.g., 1), the NUT value of the VCL NAL unit for two or moresubpictures may be configured as shown below. The following descriptionis for illustrative purposes only and is not limited thereto.

Combination 1) IRAP+non-IRAP (inter)

Combination 2) non_IRAP (inter)+non-IRAP (inter)

Combination 3) IRAP+IRAP=IDR+CRA (limited by embodiment)

Combination 1) is an embodiment in which at least a subpicture in apicture has an IRAP (IDR or CRA) NUT value, and at least one othersubpicture has a non-IRAP (inter slice) NUT value. Here, a valueexcluding the LPs (RASL and RADL) may be allowed as an inter slice NUTvalue. For example, an LP (RASL or RADL) may not be allowed as the interslice NUT value. In this manner, it may be restricted so that the RASLand RADL subpictures are not encoded in a bitstream associated with theIDR or CRA subpicture.

In another embodiment, only a TRAIL value may be allowed as the interslice NUT value. Alternatively, in another embodiment, all inter sliceVCL NUTS may be allowed as the inter slice NUT value.

Combination 2) is an embodiment in which at least a subpicture in apicture has a non-IRAP (inter slice) NUT value, and at least one othersubpicture has a different non-IRAP (inter slice) NUT value. Forexample, at least a subpicture may have a RASL_NUT value while at leastone other subpicture has a RADL_NUT value. In the case of an embodimentaccording to combination 2, restrictions described below may be appliedaccording to embodiments.

-   -   In one embodiment, LPs (RASL and RADL) and a non-LP (TRAIL) may        not be used together. For example, the NUT of at least one other        subpicture may not be TRAIL while the NUT of at least a        subpicture is RASL (or RADL). When the NUT of at least a        subpicture is RASL (or RADL), RASL or RADL may be used as the        NUT of at least one other subpicture. For example, the leading        subpicture of an IRAP subpicture may be forced to be a RADL or        RASL subpicture.    -   In another embodiment, LPs (RASL and RADL) and a non-LP (TRAIL)        may be used together. For example, while at least a subpicture        is RASL (or RADL), at least one other subpicture may be TRAIL.    -   In another embodiment, exceptionally in the case of condition        2), all subpictures may have the same inter slice NUT value. For        example, all subpictures in a picture may have a TRAIL NUT        value. As another example, all subpictures in a picture may have        a RASL (or RADL) NUT value.

Combination 3) shows an embodiment in which all subpictures or slices ina picture are configured of IRAP. For example, when the NUT value for aslice in a first subpicture is IDR_W_RADL, IDR_N_LP, or CRA_NUT, the NUTvalue for a slice in a second subpicture may be configured of a valueamong IDR_W_RADL, IDR_N_LP, and CRA_NUT, which is not the NUT of thefirst subpicture. For example, while a NUT value for a slice in at leasta subpicture is IDR, a NUT value for a slice in at least one othersubpicture may be configured as CRA.

Meanwhile, according to embodiments, application of an embodiment suchas Combination 3 may be limited. In an embodiment, all picturesbelonging to an IRAP or GDR access unit may be restricted to have thesame NUT. That is, when the current access unit is an IRAP access unitconfigured of only IRAP pictures, or the current access unit is a GDRaccess unit configured of only GDR pictures, it may be restricted sothat all pictures belonging thereto may have the same NUT. For example,it may be restricted so that while the NUT value for a slice in at leasta subpicture is IDR, the NUT value for a slice in at least one othersubpicture is not configured as CRA. In this manner, when combination 3)is restricted and the combination 1) and combination 2) described aboveare applied, it may be restricted so that at least a subpicture in thecorresponding picture may have a NUT value for a non-IRAP (inter slice).For example, in the encoding and decoding process, it may be restrictedso that all subpictures in a corresponding picture may not have a NUTvalue for IDR. Alternatively, it may be restricted so that somesubpictures in a corresponding picture have a NUT value for IDR, andother subpictures may not have a CRA NUT value.

Hereinafter, syntax and semantics related to signaling of encodedinformation when a mixed NAL unit type (NUT) is applied in a picturewill be described. In addition, a decoding process using the syntax andsemantics will be described. As described above, whenmixed_nalu_type_in_pic_flag=1, a picture described by a NUT may mean asubpicture (see Table 3).

Meanwhile, as described above, when the value ofmixed_nalu_type_in_pic_flag indicates that a mixed NUT is applied, apicture may be split into at least two subpictures. Accordingly,information on the subpictures for the picture may be signaled through abitstream. In this sense, mixed_nalu_type_in_pic_flag may indicatewhether the current picture is split. For example, when the value ofmixed_nalu_type_in_pic_flag indicates that a mixed NUT is applied, itmay indicate that the current picture is split.

Hereinafter, it will be described with reference to the syntax shown inFIG. 14. FIG. 14 is a view showing an embodiment of syntax of a pictureparameter set (PPS). For example, a flag (e.g.,pps_no_pic_partition_flag) indicating whether the current picture issplit through a bitstream may be signaled through the picture parameterset (PPS). A value indicating enabled of pps_no_pic_partition_flag(e.g., 1) may indicate that split of picture is not applied to picturescurrently referencing the PPS. A value indicating disabled ofpps_no_pic_partition_flag (e.g., 0) may indicate that split of pictureusing slices or tiles may be applied to the pictures currentlyreferencing the PPS. In this embodiment, when the value ofmixed_nalu_type_in_pic_flag indicates that a mixed NUT is applied, thevalue of pps_no_pic_partition_flag may be forced to a value indicatingdisabled (e.g., 0).

When pps_no_pic_partition_flag indicates that the current picture may besplit, information on the number of subpictures (e.g.,pps_num_subpics_minus1) may be obtained from the bitstream.pps_num_subpics_minus1 may indicate a value obtained by subtracting 1from the number of subpictures included in the current picture. Whenpps_no_pic_partition_flag indicates that the current picture is notsplit, the value of pps_num_subpics_minus1 may not be obtained from thebitstream and may be derived as 0. According to the information on thenumber of subpictures determined like this, encoded information for eachsubpicture may be signaled as much as the number of subpictures includedin a picture. For example, a subpicture identifier (e.g., pps_subpic_id)for identifying each subpicture and/or the value of a flag(subpic_treated_as_pic_flag[i]) indicating whether the encoding/decodingprocess of each subpicture is independent may be determined andsignaled.

The mixed NUT may be applied when a picture is configured of two or moresubpictures. At this point, the value of a flag(subpic_treated_as_pic_flag[i]) indicating whether the encoding/decodingprocess of each subpicture is independent may be determined and signaledas many as the number of subpictures (i) included in a picture. That asubpicture is independently decoded indicates that decoding is performedby treating the subpicture as a separate picture. That is, when thevalue of the flag is “on” (e.g., subpic_treated_as_pic_flag=1), thecorresponding subpicture may be decoded to be independent from the othersubpictures in all the other decoding processes except an in-loop filterprocess. Contrarily, when the value of the flag is “off” (e.g.,subpic_treated_as_pic_flag=0), the corresponding subpicture may refer tothe other subpictures in the picture in the inter prediction process.Here, a separate flag may be set for the in-loop filter process tocontrol whether a subpicture is independent from or refers to othersubpictures. The corresponding flag (subpic_treated_as_pic_flag) may bedefined at a position of one or more among SPS, PPS, and PH. Forexample, when the flag is defined in the SPS, the flag may be named assps_subpic_treated_as_pic_flag.

In addition, in the present invention, when there are different NUTs ina picture (e.g., mixed_nalu_type_in_pic_flag=1), each subpicture in thepicture should be independently encoded/decoded due to thecharacteristic that heterogeneous NUTs should be used for thesubpictures in a picture. For example, in the case of a picture in whichmixed_nalu_type_in_pic_flag=1, when one or more inter (P or B) slicesare included in the picture, the subpic_treated_as_pic_flag value of allsubpictures in the picture may be forced to be set to “1” or to bedriven to a value of “1”. Alternatively, whenmixed_nalu_type_in_pic_flag=1, subpic_treated_as_pic_flag may be forcednot to have a value of “0”. For example, in the case of a picture inwhich mixed_nalu_type_in_pic_flag=1, when one or more inter slices areincluded in the picture, the value of subpic_treated_as_pic_flag may bereset to “1” for all subpictures of the picture regardless of a parsedvalue. Contrarily, in the case of a picture in whichmixed_nalu_type_in_pic_flag=1 and subpic_treated_as_pic_flag=0 for allsubpictures in the picture, an inter slice should not be included in thepicture. That is, in the case of a picture in whichmixed_nalu_type_in_pic_flag=1 and subpic_treated_as_pic_flag=0, theslice type in the picture should be intra.

In addition, in another embodiment, in the case wheremixed_nalu_type_in_pic_flag=1, when the NUT of the current picture isRASL, subpic_treated_as_pic_flag for the current picture may be forcedto be set to “1”. As another example, in the case wheremixed_nalu_type_in_pic_flag=1, when the NUT of the current picture isRADL and the NUT of a referenced picture is RASL,subpic_treated_as_pic_flag for the current picture may be forced to “1”.

The mixed NUT function may restrict all subpictures (or slices) in apicture from being configured of IRAP. At this point, the value of aflag (gdr_or_irap_pic_flag) indicating that all slices in a picture areconfigured of IRAP or that a corresponding picture is a GDR (GradualDecoding Refresh) picture may be forced to “0”. That is, in the presentinvention, when there is another NUT in a picture(mixed_nalu_type_in_pic_flag=1), the value of the flag(gdr_or_irap_pic_flag) may be set to “0” or may be derived as a value of“0”. Alternatively, when mixed_nalu_type_in_pic_flag=1,gdr_or_irap_pic_flag may be forced not to have a value of “1”. The flag(gdr_or_irap_pic_flag) may be defined at a position of one or more amongSPS, PPS, and PH.

In addition, as the mixed NUT function is applied, at least a subpicturein a picture may have an IRAP (IDR or CRA) NUT value, and at least oneother subpicture may have a non-IRAP (inter slice) NUT value. That is,intra slices and inter slices may exist in a picture at the same time.In the case of the existing HEVC standard, when the NUT of acorresponding intra slice is IDR, the DPB is reset. Accordingly, allreconstructed pictures existing in the DPB at the time point areremoved.

However, according to the present invention, whenmixed_nalu_type_in_pic_flag=1, since intra slices and inter slices mayexist in a picture at the same time, there is a case in which the DPBmay not be reset although a picture is an IDR NUT. Accordingly, in anembodiment, when a corresponding slice is an IDR NUT, reference pictureinformation (RPL: reference picture list) may be inserted in the NALbitstream as slice header information of a corresponding IDR, like theCRA. To this end, although a corresponding slice is an IDR NUT, thevalue of a flag (idr_rpl_present_flag) indicating existence of RPLinformation may be set to “1”. When the value of the flag(idr_rpl_present_flag) is “1”, the RPL exists as slice headerinformation of the IDR. Contrarily, when the value of the flag(idr_rpl_present_flag) is “0”, the RPL does not exist as slice headerinformation of the IDR.

Meanwhile, in the present invention, when another NUT exists in apicture (mixed_nalu_type_in_pic_flag=1) and the RPL information of anIDR picture is not allowed (idr_rpl_present_flag=0), the NUT for thepicture may not have a value of IDR_W_RADL or IDR_N_LP.

The flag (idr_rpl_present_flag) may be defined at a position of one ormore among SPS, PPS, and PH. For example, when the flag is defined inthe SPS, the flag may be named as sps_idr_rpl_present_flag. For example,although the NUT of the current slice is IDR_W_RADL or IDR_N_RADL, sliceheader information may be signaled using the syntax of the slice headerin FIG. 15 in order to signal the RPL according to the value ofsps_idr_rpl_present_flag. Here, a first value (e.g., 0) ofsps_idr_rpl_present_flag may indicate that the RPL syntax element maynot be provided by the slice header of a slice of which the NUT isIDR_N_LP or IDR_W_RADL. A second value (e.g., 1) ofsps_idr_rpl_present_flag may indicate that the RPL syntax element may beprovided by the slice header of a slice of which the NUT is IDR_N_LP orIDR_W_RADL.

Meanwhile, in another embodiment, when mixed_nalu_type_in_pic_flag=1,the RPL may be signaled as picture header information. For example, inthe application of the syntax shown in FIG. 14, when the value ofmixed_nalu_type_in_pic_flag indicates that a mixed NUT is applied, thevalue of pps_no_pic_partition_flag may be forced to a value indicatingdisabled (e.g., 0). Accordingly, the value of a flag(pps_rpl_info_in_ph_flag) indicating whether the RPL information isprovided from the picture header may be obtained from a bitstream. Whenpps_rpl_info_in_ph_flag indicates enabled (e.g., 1), the RPL informationmay be obtained from the picture header as shown in FIGS. 16 and 17. Inthis way, the RPL information may be obtained regardless of the type ofa corresponding picture based on the value ofmixed_nalu_type_in_pic_flag. On the other hand, whenpps_rpl_info_in_ph_flag indicates disabled (e.g., 0), the RPLinformation may not be obtained from the picture header. For example,when the slice NUT is IDR_N_LP or IDR_W_RADL and the value ofsps_idr_rpl_present_flag is while the value of pps_rpl_info_in_ph_flagis “0”, the RPL information of a corresponding slice may not beobtained. That is, since there is no RPL information of a correspondingslice, the RPL information may be induced as being initialized andempty.

As described above, a picture may be signaled as NAL units withdifferent types. In this way, since a NAL unit having different NUTs maybe used to signal a picture, a method for determining a type of apicture according to the type of the NAL unit is required. Accordingly,in the case of random access (RA), whether a corresponding picture canbe normally reconstructed, and output may be determined.

In the decoding process according to an embodiment, when each VCL NALunit corresponding to a picture is a NAL unit of a CRA_NUT type, thepicture may be determined as a CRA picture. In addition, when each VCLNAL unit corresponding to a picture is a NAL unit of an IDR_W_RADL orIDR_N_LP type, the picture may be determined as an IDR picture. Inaddition, when each VCL NAL unit corresponding to a picture is a NALunit of an IDR_W_RADL, IDR_N_LP, or CRA_NUT type, the picture may bedetermined as an IRAP picture.

In addition, when each VCL NAL unit corresponding to a picture is a NALunit of a RADL_NUT type, the picture may be determined as a randomaccess decodable leading (RADL) picture. In addition, when each VCL NALunit corresponding to a picture is a NAL unit of a TRAIL_NUT type, thepicture may be determined as a trailing picture. In addition, when thetype of at least one VCL NAL unit among VCL NAL units corresponding to apicture is a RASL_NUT type and the types of all the other VCL NAL unitsare a RASL_NUT type or a RADL_NUT type, the picture may be determined asa random access skipped leading (RASL) picture.

Meanwhile, in the decoding process according to another embodiment, whenat least a subpicture is RASL in a picture and at least one othersubpicture is RADL, the picture may be determined as a RASL picture. Forexample, when at least a subpicture is RASL in a picture and at leastone other subpicture is RADL, the picture may be set as a RASL picturein the decoding process. Here, when the type of a VCL NAL unitcorresponding to a subpicture is RASL_NUT, the subpicture may bedetermined as RASL. Accordingly, in the case of RA, both the RASLsubpicture and the RADL subpicture may be treated as a RASL picture, andaccordingly, the picture may not be output.

Meanwhile, in the decoding process according to another embodiment, whenat least a subpicture in a picture is RASL, the picture may be set as aRASL picture. For example, when at least a subpicture in a picture isRASL and at least one other subpicture is TRAIL, the picture may be setas a RASL picture in the decoding process. Accordingly, in the case ofRA, the picture may be treated as a RASL picture, and the picture maynot be output.

Here, occurrence of RA may be determined by the value ofNoOutputBeforeRecoveryFlag of an IRAP picture connected (related) to acorresponding inter slice (RADL, RASL, or TRAIL). When the flag value is“1” (NoOutputBeforeRecoveryFlag=1), it means occurrence of RA, and whenthe flag value is (NoOutputBeforeRecoveryFlag=0), it means a normalplayback. The flag value may be set as follows for IRAP.

-   -   The process of setting the value of NoOutputBeforeRecoveryFlag        when the current picture is IRAP

{circle around (1)} When the picture is the first picture in abitstream, NoOutputBeforeRecoveryFlag is set to “1”.

{circle around (2)} When the picture is IDR, NoOutputBeforeRecoveryFlagis set to “1”.

{circle around (3)} When the picture is CRA and RA is notified from theoutside, NoOutputBeforeRecoveryFlag is set to “1”.

{circle around (4)} When the picture is CRA and RA is not notified fromthe outside, NoOutputBeforeRecoveryFlag is set to “0”.

In an embodiment, the decoding device may receive a signal indicatingoccurrence of random access from an external terminal. For example, theexternal terminal may signal occurrence of random access to the decodingdevice by setting the value of random access occurrence information to 1and signaling the random access occurrence information to the decodingdevice. The decoding device may set the value of flagHandleCraAsClvsStartFlag indicating whether occurrence of random accessis received from the external terminal to 1 according to the randomaccess occurrence information received from the external terminal. Thedecoding device may set the value of NoOutputBeforeRecoveryFlag to avalue the same as the value of HandleCraAsClvsStartFlag. Accordingly,when the current picture is a CRA picture and the value ofHandleCraAsClvsStartFlag is “1”, the decoding device may determine thatrandom access has occurred for a corresponding CRA picture, or mayperform decoding by treating the CRA as being located at the beginningof a bitstream.

In the case of RA, the process of setting a flag (PictureOutputFlag)that determines whether to output the current picture is as follows. Forexample, PictureOutputFlag for the current picture may be set in theorder described below. Here, a first value (e.g., 0) ofPictureOutputFlag may indicate that the current picture is not output. Asecond value (e.g., 1) of PictureOutputFlag may indicate that thecurrent picture is output.

(1) When the current picture is RASL and NoOutputBeforeRecoveryFlag of arelated IRAP picture is “1”, PictureOutputFlag is set to “0”.

(2) When the current picture is a GDR picture, of which the value ofNoOutputBeforeRecoveryFlag is “1”, or is a reconstructed picturethereof, PictureOutputFlag is set to “0”

(3) Otherwise, the value of PictureOutputFlag is set to a value the sameas the value of pic_output_flag in a bitstream. Here, pic_output_flagmay be obtained at a position of one or more among PH and SH.

FIG. 18 shows an example of synthesis of three different contentspresented in the present invention. FIG. 18(a) shows sequences for threedifferent contents, and although one picture is shown as one packet forconvenience, a picture may be split into a plurality of slices, andthere may be a plurality of packets. FIGS. 18(b) and 18(c) showsynthesized image results for the picture indicated by the dotted linesin FIG. 18(a). In FIG. 18, the same color means the samepicture/subpicture/slice. In addition, the P slice and the B slice mayhave a value among inter NUTs.

As described above, in the case of synthesizing a plurality of contentsthrough the present invention, the contents may be quickly and easilysynthesized without a delay by simply setting hierarchical GOPstructures without the need of necessarily setting the positions ofintra slices (pictures).

Embodiments of Encoding and Decoding

Hereinafter, a method of decoding a video by a video decoding deviceaccording to the method described above will be described. FIGS. 19 and20 are flowcharts illustrating a decoding method and an encoding methodaccording to an embodiment of the present invention.

A video decoding device according to an embodiment may include a memoryand at least one processor and may perform the decoding method describedbelow by the operation of the processor. First, the decoding device mayobtain NAL unit type information indicating the type of a currentnetwork abstraction layer (NAL) unit from a bitstream (S1910).

Next, when the NAL unit type information indicates that the NAL unittype of a current NAL unit is an encoded data for a slice, the decodingdevice may decode the slice based on whether a mixed NAL unit type isapplied to the current picture (S1920).

Here, the decoding device may perform decoding of the slice bydetermining whether the NAL unit type of the current NAL unit indicatesthe attribute of a subpicture for the current video slice based onwhether the mixed NAL unit type is applied.

Whether the mixed NAL unit type is applied may be identified based on afirst flag (e.g., pps_mixed_nalu_types_in_pic_flag) obtained from apicture parameter set. When the mixed NAL unit type is applied, thecurrent picture to which the current slice belongs may be split into atleast two subpictures.

Furthermore, based on whether the mixed NAL unit type is applied,decoding information for a subpicture may be included in a bitstream. Inan embodiment, a second flag (e.g., pps_no_pic_partition_flag)indicating whether the current picture is not split may be obtained fromthe bitstream. In addition, when the second flag indicates that thecurrent picture may be split (e.g., pps_no_pic_partition_flag==0), athird flag (e.g., pps_rpl_info_in_ph_flag) indicating whether referencepicture list information is provided in the picture header may beobtained from the bitstream.

In this example, when the mixed NAL unit type is applied, the value ofthe second flag (pps_no_pic_partition_flag) is forced to 0 as thecurrent picture is forced to be split into at least two subpictures, andthe third flag (e.g., pps_rpl_info_in_ph_flag) indicating whether thereference picture list information is provided from the picture headermay be obtained from a bitstream regardless of the value of the secondflag (pps_no_pic_partition_flag) actually obtained from the bitstream.Accordingly, when the third flag indicates that the reference picturelist information is provided from the picture header (e.g.,pps_rpl_info_in_ph_flag==1), the reference picture list information maybe obtained from a bitstream related to the picture header.

In addition, when the mixed NAL unit type is applied, the currentpicture may be decoded based on a first subpicture and a secondsubpicture having different NAL unit types. Here, when the NAL unit typeof the first subpicture has any one value among Instantaneous DecodingRefresh With Random Access Decodable Leading (IDR_W_RADL), InstantaneousDecoding Refresh No reference Leading Picture (IDR_N_LP), and CleanRandom Access NAL Unit Type (CRA_NUT), an available NAL unit type thatcan be selected as the second subpicture NUT may include a NAL unit typethat is not selected by the first subpicture among IDR_W_RADL, IDR_N_LP,and CRA_NUT.

Alternatively, when the NAL unit type of the first subpicture has anyone value among Instantaneous Decoding Refresh With Random AccessDecodable Leading (IDR_W_RADL), Instantaneous Decoding Refresh Noreference Leading Picture (IDR_N_LP), and Clean Random Access NAL UnitType (CRA_NUT), the available NAL unit type of the second subpicture mayinclude TRAIL_NUT (Trail NAL Unit Type).

Meanwhile, when the mixed NAL unit type is applied, the first subpictureand the second subpicture constituting the current picture may beindependently decoded. For example, the first subpicture and the secondsubpicture including a B or P slice may be treated and decoded as onepicture. For example, the first subpicture may be decoded without usingthe second subpicture as a reference picture.

More specifically, a fourth flag (e.g., sps_subpic_treated_as_pic_flag)indicating whether the first subpicture is treated as a picture in thedecoding process may be obtained from a bitstream. When the fourth flagindicates that the first subpicture is treated as a picture in thedecoding process (e.g., sps_subpic_treated_as_pic_flag==1), the firstsubpicture may be treated and decoded as a picture in the decodingprocess. In this process, when the mixed NAL unit type is applied to thecurrent picture and the current picture including the first subpictureincludes at least one among the P slice and the B slice, the fourth flagmay be forced to have a value indicating that the first subpicture istreated as a picture in the decoding process. On the other hand, whenthe mixed NAL unit type is applied to the current picture and the fourthflag indicates that the first subpicture is not treated as a picture inthe decoding process (e.g., sps_subpic_treated_as_pic_flag==0), theslice type belonging to the current picture should be intra.

When the fourth flag indicates that the first subpicture is treated as apicture in the decoding process, it may be determined that the decodingprocess of the first subpicture is independent from those of the othersubpictures. For example, when the fourth flag indicates that the firstsubpicture is decoded to be independent from the other subpictures inthe decoding process, the first subpicture may be decoded without usingother subpictures as a reference picture.

In addition, when the first subpicture is a Random. Access SkippedLeading (RASL) subpicture, the current picture may be determined as aRASL picture based on whether the second subpicture is a Random. AccessDecodable Leading (RADL) subpicture. Here, when the type of a NAL unitcorresponding to the first subpicture is a Random Access Skipped LeadingNAL Unit Type (RASL_NUT), the first subpicture may be determined as aRASL subpicture.

In addition, when the third flag (e.g., pps_rpl_info_in_ph_flag)indicates that the reference picture list information may be obtainedfrom the slice header (e.g., pps_rpl_info_in_ph_flag==0) rather than thepicture header, and the NAL unit type of the first subpicture has anyone value among Instantaneous Decoding Refresh With Random AccessDecodable Leading (IDR_W_RADL) and Instantaneous Decoding Refresh Noreference Leading Picture (IDR_N_LP), the reference picture listinformation may be obtained from a bitstream related to the sliceheader, based on a fifth flag (e.g., sps_idr_rpl_present_flag)indicating whether or not the reference picture list information for anIDR picture may exist in the slice header. Here, the fifth flag may beobtained from a bitstream related to a sequence parameter set.

Meanwhile, in the case where random access is performed for an IntraRandom Access Point (IRAP) picture related to the current picture, whenthe current picture is a Random Access Skipped Leading (RASL)subpicture, the current picture may not be output (displayed).

A video encoding device according to an embodiment may include a memoryand at least one processor and may perform an encoding methodcorresponding to the above-described decoding method by the operation ofthe processor. For example, when a current picture is encoded based on amixed NAL unit type, the encoding device may determine a type ofsubpicture for splitting the picture (S2010). In addition, the encodingdevice may generate a current NAL unit by encoding at least one currentslice constituting the subpicture based on the type of the subpicture(S2020). At this point, when the current picture is encoded based on themixed NAL unit type, the encoding device may encode a slice by encodingso that the NAL unit type of the current NAL unit indicates theattribute of the subpicture for the current slice.

In addition, the present invention may be implemented on acomputer-readable recording medium as a code that can be read by acomputer (including all devices having an information processingfunction). The computer-readable recording medium includes all types ofrecording devices for storing data that can be read by a computersystem. Examples of the computer-readable recording devices include ROM,RAM, CD-ROM, magnetic tapes, floppy disks, and optical data storagedevices.

Although the present invention has been described with reference to theembodiments shown in the drawings, these are merely exemplary, and thoseskilled in the art will appreciate that various modifications andequivalent other embodiments are possible therefrom. Therefore, the truescope of the present invention should be determined by the spirit of theattached claims.

What is claimed is:
 1. A video decoding method performed by a videodecoding device, the method comprising the steps of: obtaining a firstflag indicating whether a current picture includes subpictures havingdifferent network abstraction layer (NAL) unit types; and obtainingsecond flags respectively corresponding to the subpictures, wherein eachof the second flags indicates whether a corresponding subpicture istreated as a picture in a decoding process, when the first flagindicates that the current picture includes subpictures having differentNAL unit types, second flags for all subpictures having a NAL unit typeequal to RASL (Random Access Skipped Leading) among the subpictures arerestricted to have a first value regardless of whether each subpicturewhose NAL unit type is equal to RASL is referenced, and the first valueindicates that the corresponding subpicture is treated as a picture in adecoding process.
 2. The method according to claim 1, wherein, in adecoding process excluding in-loop filtering, a subpicture whose secondflag is equal to the first value is treated as a picture and decoded tobe independent from other subpictures.
 3. The method according to claim1, wherein, when a first NAL unit of the picture has the NAL unit typeequal to IDR or CRA, a second NAL unit of the picture is restricted tohave the NAL unit type excluding RASL and RADL.
 4. The method accordingto claim 3, the second NAL unit has the NAL unit type equal to one ofIDR and CRA, and the NAL unit type of the second NAL unit is differentfrom the NAL unit type of the first NAL unit.
 5. The method according toclaim 3, the second NAL unit has the NAL unit type equal to TRAIL. 6.The method according to claim 1, wherein, when the picture includes asubpicture having a NAL unit type equal to RASL and another subpicturehaving a NAL unit type equal to RADL (Random Access Decodable Leading),the picture is treated as a RASL picture in a decoding process.
 7. Themethod according to claim 6, wherein the RASL picture is not output.